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Mammals

If maximum animal size can serve as a valid paleogravity indicator, then gravity reached its minimum - 0.8 g - during the Late Jurassic when the largest dinosaurs existed. Since gravity today is higher, gravity must have increased between the Late Jurassic and the present, in conjunction perhaps with a contraction of the Earth. During the Cretaceous Period, dinosaurs were generally smaller than their Jurassic forebears. (Bakker contrasts the 'high browsers' of the Jurassic with the 'low...

Practically all the work done in walking and running is against gravity. When American astronauts went to the Moon in the late 1960s and early 1970s, they discovered that walking and running, the normal bipedal gaits of humans on Earth, were ineffective on the Moon where gravity is 1 6 that of Earth. But the astronauts discovered that by modifying their locomotive behavior, and shifting to a skipping or hopping gait, they could move about quickly with relatively little effort or exertion. The...

The reason predatory dinosaurs became bipedal is not at all clear. The only thing that can be said in the end is that bipedalism was a serendipitously crucial adaptation The earliest known biped was the Early Triassic thecodont Euparkeria. Fig. 4A . Though normally quadrupedal, this small reptile was capable of shifting to a bipedal gait when moving quickly. In the Middle and Late Triassic, bipedality became increasingly common among the thecodonts and evolved independently in several lineages...

If gravity were halved, we should get a lighter, slenderer, more active type needing less energy, less heat, less heart, less lungs, less blood. Any comprehensive theory of dinosaur evolution must also tackle the problem of mammal origins and evolution. Dinosaurs and mammals both originated during the Late Triassic. For 140 million years, the dinosaurs were the preeminent land vertebrates while our ancestors endured a long 'mammalian dark age' that ended only when the dinosaurs went extinct at...

The sauropods began their long evolutionary history as giants one might say that geologically speaking they became instantaneous giants, because the first of these great dinosaurs is found in rocks of very early Jurassic age. Barapasaurus, from the Early Jurassic, was one of the first true sauropods. At twenty-five meters in length,54 Barapasaurus was the largest animal that had yet evolved. Prior to the Mesozoic, the largest land animals were herbivorous pelycosaurs from the Permian, sprawling...

Table 1 - Comparison of Similarity Formulas10 Table 1 - Comparison of Similarity Formulas10 7 Galilieo, 1638, 1954 edition. 8 McMahon, 1973 Rashevsky, 1960. Each of these scaling formulas can, within limited domains, account for the known facts, but none of them is universally valid. Leg dimensions in adult ungulates, for example, seem to be scaled for elastic similarity but those of mammals in general are not. Mammalian leg lengths correspond more closely to the value predicted by geometric...

90 of the genera other reptiles seem for the most part to have been crowded out. And despite mass extinctions at the end of the Permian, the mammal-like reptiles were still very common in the Early Triassic. Yet by the end of the Triassic, the therapsids were all but extinct and the world belonged to dinosaurs. See Figure 1. Therapsids and dinosaurs belonged to two distinct subclasses of reptiles the therapsids were synapsid reptiles and the dinosaurs were diapsids. Synapsid and diapsid...

The coincidence in time of incipient rifting of Pangea and the origin of dinosaurs during the Carnian age 230-225 Ma of the Late Triassic suggests a fundamental link between the two. That link may have been the onset of Earth expansion, triggered by the Pangean thermal anomaly and resulting in a 20 reduction in surface gravity. In reduced gravity, animals will have less skeletal mass and thinner bones than equally massive animals adapted to normal gravity a significant increase in maximum body...